Unilateral pneumonectomy in laboratory animals induces a stimulus to the growth of the remaining lung such that lung volume greatly increases above normal. The main thrust of the research is to ascertain the effects of air pollutant gases on this accelerated lung development and to determine whether growth is impaired on exposure to pollutants in concentrations found in urban environments. The characterization of this "stimulated" lung development in control animals and in animals exposed to ozone and other oxidants will be derived from measurements of pulmonary function, from morphometry by light and electron microscopy and from biochemical analyses. The experimental design offers the advantage of investigating the effects of environmental stress on a compromised organ in a state of change. The findings may have particular significance in the areas of neo-natal development and pneumonectomy in the adult.